This invention relates in general to a process for rolling H-shaped metallic materials, and more particularly to a hot rolling process which allows efficient production of H-shaped metallic materials from starting materials of rectangular cross section.
The following describes the present invention in conjunction with the rolling of steel as a typical metallic material, so that the finished product will be referred to as H-shaped steel or an H-beam and the starting material, as a steel slab, bloom, billet or the like, as required. It is also to be noted that the H-shaped steel herein involves not only ordinary H-shapes but also other H-shapes similar thereto.
In the rolling of H-shapes which are relatively large in cross-sectional area and over 100 mm in flange width, it has so far been a common practice that a beam blank having a configuration resembling the shape of the H-beam to be produced is used as starting material and is rolled into the intended H-shape by a two-high roughing rolling mill and a plurality of universal rolling mills. FIG. 1 illustrates the cross-sectional shape of an exemplary beam blank 1 employed in the prior art. FIG. 2 shows an exemplary rolling system layout according to the prior art. In this arrangement, a two-high roughing rolling mill 11 is followed by universal rolling mills 12, 13 and 14, and edging mills 15 and 16 are added to the universal rolling mills 12 and 13 on the respective entry sides thereof. In the rolling system shown in FIG. 2, a beam blank 1 heated to a rolling temperature and conveyed on a roller table 10 is first subjected to roughing in the roughing rolling mill 11 and then undergoes intermediate rolling and finishing rolling in the universal rolling mills 12, 13 and 14 so as to be finished to a required size. In the universal rolling mill 12 for example, the horizontal rolls 12H depress the web surfaces of the workpiece while the vertical rolls 12V depress the flange surfaces thereof. The edging mills 15 and 16 reduce the flange tips to form flanges of a desired width.
Such a rolling method, however, necessitates the use of grooved rolls in the breakdown step for beam blank production and therefore requires 90.degree. turns of the workpiece and an increased number of times of passage of the material between rolls, with a consequent great decrease in rolling efficiency.
For the purpose of efficient rolling, therefore, it is desirable to employ a starting material of rectangular cross section in place of a beam blank.
Based on this concept, a process has already been devised for rolling a starting material of rectangular cross section in universal rolling mills from the beginning, as exemplified in FIG. 3. As shown, a rectangular cross section material 3 is rolled into an H-shaped product 7 having a web portion 8 formed by horizontal rolls 21 and flange portions 9 formed by vertical rolls 23. The horizontal rolls 21 are forcedly driven to rotate around the respective axes 22 while the vertical rolls 23 are not forcedly driven but rotate as followers around the respective axes 24 through frictional contact with the workpiece.
However, this rolling process is also beset with the following problems:
(a) This process is more advantageous in the lateral spreading of the flanges than the rolling by two-high type rolls. Nevertheless, this method also requires the starting material to have a larger thickness than the flange width of the finished product.
(b) Hence, the rolling reduction in the web portion by the horizontal rolls is so large that, as shown in FIG. 4, the web portion 8 extends at both the front and rear ends thereof to form a crop "C" at each end, thus lowering the yield.
(c) Generally, the starting material tends to have a relatively large cross-sectional area, and the material elongation to the final length tends to increase. Thus, difficulties in rolling may be encountered for reasons concerning equipment conditions.
More particularly, there is a limit to the length of the rolling line in view of the necessity of an elongated building, a sawing machine, an increased number of times of material passage between rolls, and so forth. Thus, the cross-sectional area of the starting material is limited by the length of the rolling line. Conversely, it can be considered to lessen the length of the starting material corresponding to an increase in the cross-sectional area of the starting material. In this case, however, as compared with the length of a heating furnace, the length of the material may become so short as to cause a significant decrease in the efficiency of the furnace.